This invention relates to a drive control system for a hydraulic machine, specifically, to a drive control system equipped with an electric lever device for controlling the hydraulic actuator of a machine such as a hydraulic shovel.
A machine such as a hydraulic shovel is generally equipped with plural hydraulic actuators. These hydraulic actuators are individually controlled by corresponding actuation control devices which include a manipulation lever device. Specific examples of the actuation control device may include those making use of an electric lever device. Such an electric lever device has a manipulation lever and an output device for generating an electrical manipulation signal corresponding to the degree of manipulation of the lever (for example, a potentiometer), a control valve connected to a hydraulic circuit for actuating a hydraulic actuator, a controller unit having a main controller for receiving the manipulation signal from the electric lever device and computing a control signal for the control valve on the basis of the manipulation signal, and an output device for generating an electrical actuation signal corresponding to the control signal. A main power supply is also provided to drive the controller unit. The controller unit includes a power supply for the main controller and another power supply for the output device. The power supplies are both connected to the main power supply. For plural hydraulic actuators, the corresponding number of control valves, electric lever devices, and output devices of the controller unit are provided.
In such a drive control device, the controller unit is brought into a driven state upon connection of the main controller's power supply and the power supply for the output devices to the main power supply. When the manipulation lever is moved in a given degree from the neutral position, an electrical signal corresponding to the degree of manipulation of the lever is outputted from the potentiometer to the controller unit so that an electrical actuation signal corresponding to the manipulation signal is produced by the main controller and output device of the controller unit. Where the control valve is a solenoid-operated valve, the solenoid-operated valve is actuated directly by the actuation signal. Where the control valve is a hydraulic pilot-operated valve, the electrical actuation signal is converted to a hydraulic signal by an electrical signal/hydraulic signal converter to actuate the hydraulic pilot-operated valve. In response to the actuation of the control valve, the hydraulic actuator is actuated to drive the working member with which the hydraulic actuator is associated.
Where the hydraulic machine is a construction machine (for example, a hydraulic shovel for digging or excavating the earth), the above--mentioned hydraulic actuators are a boom cylinder, an arm cylinder, a bucket cylinder, a swivel motor, etc. The aforementioned working members include a boom driven by the boom cylinder, an arm driven by the arm cylinder, a bucket driven by the bucket cylinder, a swivel cabin driven by the swivel motor, etc.
If a certain problem occurs or if work-induced noise causes jamming in the controller unit, a signal conductor between the electric lever device and the controller unit, or the electric lever device of the above-described conventional drive control system, a false signal may be outputted from the output device of the controller unit to the control valve so that even after the manipulation lever has been shifted back to the neutral position, the control valve takes an actuated position different from the center valve position. As a result, the associated hydraulic actuator and working member are not at their initial positions corresponding to the neutral position of the manipulation lever, leading to a possible safety hazard. Such problems tend to occur especially where a construction machine such as the above-mentioned hydraulic shovel is used, because its working environment is usually severe.
DE A-2631530 discloses a drive control system equipped with an electric lever device in which the electric lever device is provided with a switch for sensing the neutral position of a manipulation lever. While the manipulation lever is at the neutral position, the switch is kept open so as to inhibit the actuation of a manipulation signal output device. Let's assume that such a problem, or noise jamming, has occurred in the electric lever device and a false signal is about to be outputted as a result. The above construction opens the switch when the manipulation lever is shifted back to the neutral position. The actuation of the output device is hence inhibited to avoid the output of the false signal. The safety of the work is hence ensured.
However, in the conventional system described above, the prevention of a false signal occurring due to trouble, or jamming caused by noise or similar trouble is limited to the electric lever device. The conventional system cannot inhibit the output of a false signal when the false signal is produced due to occurrence of trouble, jamming caused by noise or similar trouble in a signal conductor downstream of the electric lever device or in the controller unit. Even when the manipulation lever is at the neutral position, the control valve is actuated to drive the associated hydraulic actuator and working member, resulting in the problem that safety cannot be assured.